DESCRIPSTION: (Adapted from the Investigator's Abstract) The investigators propose to conduct a prospective cohort study to address three primary hypotheses: 1) weight gain, adjusted for height growth, is positively related to inactivity and intake of fat and energy, and inversely related to activity; 2) adolescent activity patterns, including inactivity, are related to age, gender, social influences and (both present and past) parental activity patterns; 3) physical activity decreases through adolescence and adolescent diet is influenced by factors both within the family and in society at large. In particular, adolescents who prepare more of their own meals or who consume more meals away from home have higher fat intake and lower intake of fruit and vegetables, compared with other adolescents; and mothers' food and nutrient intake influences their children's intakes. During adolescence this influence decreases over time. To accomplish this the investigators will enroll 11,000 children of participants in their ongoing Nurses' Health Study II. Eligible children will be between ages 10 and 14 and will be comprised of African-American (approximately 8%), Asian (8%), Hispanic (8%), and (76%) white girls. They will collect information on diet, activity and inactivity as well as weight, height, by means of a mailed questionnaire. Follow-up questionnaires will be mailed annually to update information on diet and activity and to ascertain current height and weight. This proposed study will be closely patterned after the investigators ongoing Nurses' Health Studies, but will address issues relating to weight gain, adjusted for height, in adolescence, issues that cannot be addressed through the ongoing studies in which the youngest women are 31. This new cohort will take advantage of the investigators' considerable experience and resources developed in the conduct of the Nurses' Health Studies, and experience of co-investigators in assessing behaviors among children and adolescents. This includes not only the expertise of the investigators, but also the skills of their programmers and other support staff, computing and data processing facilities, and an extensive body of management and analysis of software especially designed for large cohort studies. Through this effort they hope to identify the relations among the modifiable causes of weight gain.